Block copolymer (BCP) lithography has emerged as a promising tool to create highly regular and dense dot or line arrays at sub 50 nm length scales. Block copolymer lithography refers to the use of self-assembled domain structures, typically spheres, cylinders, and lamellas in the form of a thin film as a template for addition and subtraction nanofabrication processes. Two pattern geometries have been the focus of BCP studies: dense arrays of dots; and dense arrays of lines and spaces. The former can be generated from sphere-forming BCPs or from cylinder-forming BCPs with domains oriented perpendicular (vertical) with respect to the substrate surface, and the latter from cylinder-forming BCPs with domains oriented parallel with respect to the substrate surface or lamella-forming BCPs with domains oriented vertically with respect to the substrate surface. However, lamellae and cylinders that are oriented perpendicular (vertical) with respect to the underlying substrate surface may have advantages in pattern transfer applications over spheres or parallel cylinders because of the higher aspect ratio of the resulting template and the vertical side-walls.
The perpendicular alignment of block copolymer domains in thin films can be controlled by chemical modification of the substrate in the form of neutral layers that are used to induce perpendicular domain orientation. Crosslinked or grafted films of random terpolymers have been used as neutral layers for block copolymers of styrene and methyl methacrylate (e.g., P(S-b-MMA)). For example, terpolymers of styrene, methyl methacrylate and a third crosslinkable co-monomer, such as hydroxyl methacrylate (HEMA) or glycidyl methacrylate (GMA), have been used as neutral (nonpreferential) surfaces for the formation of vertical domains in an overlying block copolymer. However, in the design of these terpolymer-based neutral layers, adjusting the interfacial energy between the neutral layer surface and the P(S-b-MMA) was accomplished by changing the amount of styrene and MMA in the random copolymer. The amount of the crosslinkable third monomer (e.g., GMA) was fixed at a low level, since this monomer was used to provide crosslinking and not to control wetting properties.